It is known for the production of non-woven fabrics that the fibers are laid down to a fiber layer on a laydown belt by means of an air flow. This method, ordinarily described as air laid among experts, is based on the fact that the fibers or fiber mixtures are placed uniformly distributed on the surface of a laydown belt by means of a forming head. The zone covered by the forming head on the laydown belt is ordinarily referred to as a forming zone, in which the fibers meet on the laydown belt. Such a method and device are described in, for example, WO 2004/106604 A1. In the case of the known methods and the known device, a multiplicity of fibers or fiber mixtures is fed to a forming head by means of an air flow. Within the forming head means are provided for mixing and distributing the fibers. On the underside of the forming head a forming outlet is constructed which ordinarily is arranged at a short distance above the laydown belt. In this connection, a clearance is formed between the forming head and the laydown belt, the clearance serving to guide a fiber stream escaping from the forming outlet. The laying down of the fibers on the laydown belt is supported by a suction device which absorbs the air of the fiber stream and conducts it away. The fiber layer forming on the surface of the laydown belt is continuously conveyed via the laydown belt out of the forming zone, so that a fiber layer is formed which is subsequently fed to a further treatment, for example solidification.
Depending on the fiber type and fiber size used in such methods, irregularities can arise in the laying down of the fibers, with the irregularities being referred to as beaching. Such irregularities in the fiber distribution are generally attributed to the fact that the distribution and laying down of the fibers is influenced by secondary air flows from the surroundings which are absorbed from the surroundings into the forming zone via the suction device.
In order to eliminate such irregularities in the laying down of the fibers, it is known for example from WO 2006/131122 A1 to influence the suction flow of the suction device in sub-regions of the forming zone. In the case of the known methods and the known device, a guide plate is assigned on an inflow side of the forming zone of the suction device, with the guide plate influencing the suction flow underneath the laying down belt. It is noted that air turbulence arising through suctioned secondary air from the surroundings on the inflow side of the forming zone is supposed to be prevented. However, as a result of the use of such a guide plate, there are differing suction flows in the forming zone which leads to differing laydown behavior of the fibers within the forming zone.
The phenomenon of beaching also could not be ruled out from other systems, such as those known for example from WO 2003/016622 A1. In this connection, the forming head on the inflow side and the outflow side each have sealing rollers, which are in contact with the surface of the laydown belt or the surface of the fiber layer. As a result, it possible to prevent to a great extent an influx in the secondary air from the surroundings. However, in this connection it is disadvantageous that the fiber layer on the surface of the laydown belt is condensed directly on the outflow side by the sealing roller arranged there.